<!doctype html>
<html lang="en">
    <head>
        <script>
            var script = document.createElement('script');
            // Don't do this at home kids! The "document.referrer" part is actually inserting a XSS security.
            // We are OK in this precise case because the HTML page is hosted on the "maps" domain that contains only static files.
            script.setAttribute('src', document.referrer + 'iframe_api.js');
            document.head.appendChild(script);
            window.addEventListener('load', () => {
                WA.chat.sendChatMessage('The iframe opened by a script works !', 'Mr Robot');
            })
        </script>
    </head>
    <body>
        <p>Website opened by script.</p>
    </body>
</html>